1. Field of the Invention
The present invention relates to a semiconductor laser device in which a waveguide in a resonator has current noninjection regions in vicinities of end facets. The present invention also relates to a process for producing such a semiconductor laser device.
2. Description of the Related Art
Currently, semiconductor laser devices are widely used as light sources for optical information equipment. In particular, high output power and reliability are required in semiconductor laser devices which are used in write-once and erasable optical disk drives and the like.
One of the factors which decreases the reliability of the semiconductor laser devices is degradation or damage of laser-light-emission end facets caused by heat generation. In order to solve this problem, the Japanese Unexamined Patent Publication No. 2(1990)-239679 discloses a method for realizing a current noninjection region in a vicinity of a laser-light-emission end facet of a semiconductor laser device and suppressing Joule heat generation in the vicinity of the laser-light-emission end facet. However, according to the disclosed method, a current blocking layer of made GaAs as a direct transition semiconductor material is formed in the vicinity of the laser-light-emission end facet of the semiconductor laser device. Therefore, light absorption occurs in the current blocking layer, and thus it is impossible to achieve a satisfactory current-optical output characteristic.
The registered Japanese Patents Nos. 2833962 and 2879875 disclose methods for easily realizing current noninjection in a vicinity of a laser-light-emission end facet and achieving a satisfactory current-optical output characteristic. In these methods, in order to realize a current noninjection region in the vicinity of the laser-light-emission end facet, and prevent degradation of the vicinity of the laser-light-emission end facet in which heat generation is likely to occur, a portion of a p-type GaAs contact layer in the vicinity of the laser-light-emission end facet is removed by etching so that a steplike elevation change and an overhanging profile of a surface of an electrode base layer are produced in an electrode base layer or layers on which electrodes are formed, the steplike elevation change separates an electrode for current injection from an electrode formed in the vicinity of the laser-light-emission end facet, and current in the vicinity of the laser-light-emission end facet is substantially stopped by the separation of the electrodes.
Incidentally, the cooling efficiency in the junction-down mounting is high. Therefore, in order to operate semiconductor laser devices with high output power, it is effective to junction-down mount the semiconductor laser devices on a heatsink. However, when the semiconductor laser devices disclosed in the registered Japanese Patents Nos. 2833962 and 2879875 are junction-down mounted on a heatsink, i.e., the p electrode sides of the semiconductor laser devices are bonded to the heatsink, the separated electrodes in the disclosed semiconductor laser devices are connected by soldering material, and therefore the current noninjection region cannot be realized in the vicinity of the laser-light-emission end facet. Thus, it is impossible to operate the semiconductor laser devices with high output power.
In addition, in order to separate the p side electrodes with the steplike elevation change, the p-type GaAs contact layer is required to be overetched. Therefore, it is necessary to grow the p-type GaAs contact layer to a thickness of 1.0 to 3.0 micrometers, which is greater than the thickness of the normal GaAs contact layer, 0.2 micrometers. That is, additional amounts of time, material, and energy are spent for growing such a thick contact layer. Therefore, the methods disclosed in the registered Japanese Patents Nos. 2833962 and 2879875 are not preferable from the viewpoints of productivity, energy consumption, and influence on the environment.
Further, when the p-type GaAs contact layer, which is thicker than the normal GaAs contact layer, is wet etched for removing the near-edge portions of the p-type GaAs contact layer in the vicinity of the laser-light-emission end facet, and an etching solution of NH4OH or KOH and a resist mask which is conventionally used in production of semiconductor laser devices are used for the wet etching, the resist is heavily damaged. For example, the resist deteriorates and becomes unremovable, or interpenetration between the resist and the GaAs contact layer occurs. Therefore, it is impossible to perform normal etching.